Recently, also from a standpoint of future depletion of oil resources as increasing environmental awareness, reduction of fuel consumption of cars, motorcycles, etc. is more strongly demanded than ever before. On the other hand, secondary batteries represented by lithium-ion batteries have significantly advanced, attempt of enabling electroactuation of driving power like electric cars or hybrid cars has been increasing.
However, the energy density of the secondary batteries is still infinitely smaller than one of petroleum fuel such as gasoline, and a plurality of batteries must be installed to ensure a travel distance satisfying practical use. In this regard, saddle-type vehicles such as motorcycles have originally small spaces, and ingenuity for installing a plurality of batteries in a vehicle body is required.
For example, in a scooter-type electric two-wheeled vehicle described in Patent Document 1, a large battery box is disposed to be surrounded by a main frame, a down frame, and a pivot frame of a vehicle body, and many battery cells are aligned within the box to correspond to a box's shape. Since output of the scooter-type electric two-wheeled vehicle is generally low, and just needs a small electric motor, an in-wheel electric motor integrally provided with an axle of a rear wheel is employed.
On the other hand, since a sporty electric two-wheeled vehicle is installed with a relatively large motor with high output, for example, the electric motor is often installed, in front of a pivot frame, namely at a position where an engine is conventionally installed as described in Patent Document 2. In the vehicle in this document, rotation of a motor shaft is reduced in speed by gears, and torque is increased, and transmitted to a rear wheel through a chain from an output shaft located behind the motor shaft.
In order to supply a large current to the large electric motor with high output, in the electric two-wheeled vehicle described in this document, a large energy reservoir is arranged adjacent to an upper portion of the electric motor as shown in FIG. 2. This energy reservoir is an electric storage device storing many batteries in a housing, and is located on a rear side from directly above the electric motor according to FIG. 2.